Pro-drug Compounds

ABSTRACT

A compound of formula (I), or a pharmaceutically acceptable salt thereof: 
     
       
         
         
             
             
         
       
     
     The compound is used in pharmaceutical compositions and in a method of treatment of a disease or medical condition which benefits from inhibition of gap junction activity by administering to a subject suffering from such disease or condition.

The present invention relates to neuronal gap junction blocking compounds having improved pharmacokinetic properties, the compounds being useful for the treatment or prevention of a range of conditions including migraine, epilepsy, non-epileptic seizures, brain injury (including stroke, intracranial haemorrhage and trauma induced) or cardiovascular disease including myocardial infarction, coronary revascularization or angina.

BACKGROUND TO THE INVENTION

Cortical spreading depolarization (CSD) is a wave of depolarisation with consequent depressed electrical activity which spreads across the surface of the cerebral cortex (at a rate of 2-6 mm/min) usually followed by hyperaemia and neuronal hyperpolarisation. The reduction in electrical activity is a consequence of neuron depolarisation and swelling, with K+ efflux, Na and Ca influx and electrical silence. This abnormal neuronal activity is associated with delayed neuronal damage in a number of pathological states including cerebral ischaemia (arising from e.g. stroke, haemorrhage and traumatic brain injury Strong et al., 2002 Fabricius et al., 2006; Dreier et al., 2006 Dohmen et al., 2008), epilepsy and the aura associated with migraine (Lauritzen 1994; Goadsby 2007). As the CSD wave moves across the cortex it is associated with a reactive increase in local blood flow which may serve to help restore the more normal ionic balance of the neurons affected. After the CSD induced hyperaemia the local increase in blood flow attenuates (oligaemia) potentially resulting in imbalances in energy supply and demand. Under certain conditions, the reactive hyperaemia is not observed, but instead the local vasculature constricts resulting in ischaemia which in turn can lead to neuronal death. The conditions triggering this abnormal response in experimental models are high extracellular levels of K+ and low NO availability. These conditions are typically seen in ischaemic areas of the brain, and clusters of CSD waves in these circumstances result in spreading ischaemia (see Dreier 2011). Of particular importance is the spreading ischaemia seen after sub-arachnoid haemorrhage (SAH), in the penumbra of an infarct and after traumatic brain injury where delayed neuronal damage can have a significant effect on clinical outcomes (Dreier et al., 2006, 2012; Hartings et al., 2011a, 2011b; Fabricius et al., 2006).

Given the detrimental effect of clusters of CSDs in humans and experimental animals, and the poor prognosis associated with CSDs, there is an unmet medical need for new compounds useful for inhibiting CSDs for patients with and without brain injuries. Without wishing to be bound by theory, the spread of CSD is believed to be mediated by gap junctions rather than by neuronal synaptic communication (Nedergard et al., 1995; Rawanduzy et al., 1997, Saito et al., 1997), the gap junctions providing a means of spreading the depolarisation in the absence of normal synaptic communication. Gap junctions are comprised of connexin proteins of which there are 21 in the human genome. Each Gap junction is made of two hemichannels, each comprising six connexin monomers.

Gap junctions are also implicated in a number of other disease states including hereditary diseases of the skin and ear (e.g. keratitis-ichthyosis deafness syndrome, erythrokeratoderma variabilis, Vohwinkel's syndrome, and hypotrichosis-deafness syndrome). Blockade of gap junction proteins has been shown to beneficial in some preclinical models of pain (e.g. Spataro et al., 2004 J Pain 5, 392-405, Wu et al., 2012 J Neurosci Res. 90, 337-45). This is believed to be a consequence of gap junction blockade in the spinal cord resulting in a reduction in the hypersensitivity of the dorsal horn to sensory nerve input. In addition gap junctions and their associated hemichannels have been implicated in neurodegenerative diseases including Alzheimer's disease, Parkinson's Disease, Huntington's Disease and amyotrophic lateral sclerosis (Takeuchi et al 2011 PLoS One.; 6, e21108).

Tonabersat (SB-220453/PRX201145) is a gap junction blocker (Silberstein, 2009; Durham and Garrett, 2009) which binds selectively and with high affinity to a unique stereo-selective site in rat and human brains. Consistent with its action on gap junctions Tonabersat also inhibits high K+ evoked CSD in cats (Smith et al., 2000; Read et al., 2000; Bradley et al., 2001) and rats (Read et al., 2001).

However, known gap junction blockers, including Tonabersat and Carabersat, suffer from undesirable physiochemical properties. Tonabersat is a crystalline solid with a high melting point (152-153 C) and with a relatively high lipophilicity (log P 3.32). The compound has no readily ionisable groups and consequently has a low aqueous solubility of 0.025 mg/ml over a range of pH values including pH of 7.4. The low aqueous solubility of Tonabersat makes both intravenous (IV) and oral (PO) modes of administration problematic. The poor aqueous solubility prevents rapid injection of the required dose of Tonabersat which is required for the treatment of head injuries and stroke or for emergency treatment of epileptic seizures where the patient may be unconscious and unable to swallow an oral drug. At present the effective plasma concentrations needed to reduce the cortical spreading depression caused by head injury or stroke can only be reached by slow IV infusion given over a period of hours. With respect to the PO administration of Tonabersat for the treatment of other indications, solubility limited dissolution of the tablet form of Tonabersat given PO leads to a significant “food effect” with differences in the maximum blood concentration of Tonabersat (Cmax) seen depending on whether the drug is given with or without food. These differences make it difficult to accurately predict the plasma exposure of Tonabersat when given orally, thus increasing the risk of under or over dosing the patient.

Therefore it is an object of the present invention to provide gap junction blocker compounds having improved physiochemical properties thus improving the utility of these agents in treating a range of disease states.

BRIEF DESCRIPTION OF THE INVENTION

The present invention makes available three classes of compounds, each class having one or more solubilising pro-drug groups.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention makes available a class of compounds of formula (I) or a hydrate, solvate, or pharmaceutically acceptable salt thereof:

wherein

Z₁, Z₂, and Z₃ are each independently selected from H, F, or Cl,

Q is O,

R² is H,

A is a direct bond, —C(O)O*—, —C(R³)(R⁴)O*—, —C(O)O—C(R³)(R⁴)O*—, or —C(R³)(R⁴)O—C(O)O*— wherein the atom marked * is directly connected to R¹,

R³ and R⁴ are selected independently from H, fluoro, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or

R³ and R⁴ together with the atom to which they are attached form a cyclopropyl group,

R¹ is selected from groups [1], [2], [2A], [2B][3], [4], [5] or [6] wherein the atom marked ** is directly connected to A:

R⁵ and R⁶ are each independently selected from H, C₁₋₄ alkyl, C₁₋₄ fluoroalkyl, or benzyl;

R⁷ is independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl;

R⁸ is selected from:

(i) H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or

(ii) the side chain of a natural or unnatural alpha-amino acid;

or R⁷ and R⁸ together with the atom to which they are attached form a C₃₋₇ carbocyclic ring;

R⁹ is selected from H, —N(R¹¹)(R¹²), or —N⁺(R¹¹)(R¹²)(R¹³)X⁻—, or —N(R¹¹)C(O)R¹⁴ wherein R¹¹, R¹², and R¹³ are independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 3-8 membered heterocyclic ring,

R¹⁴ is H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl,

R¹⁰ and R¹⁵ are independently selected from C₁₋₄ alkyl or C₁₋₄ fluoroalkyl,

X⁻ is a pharmaceutically acceptable anion.

In a second aspect, the present invention makes available a class of compounds of formula (II) or a hydrate, solvate, or pharmaceutically acceptable salt thereof:

wherein

Z₁, Z₂, and Z₃ are each independently selected from H, F, or Cl,

Q is O,

A is a direct bond and R¹ is H,

R² is B—R²¹ wherein,

B is a direct bond, —C(O)O*—, —C(R²³)(R²⁴)O*—, —C(O)O—C(R²³)(R²⁴)O*—, or —C(R²³)(R²⁴)O—C(O)O*— wherein the atom marked * is directly connected to R²¹,

R²³ and R²⁴ are selected independently from H, fluoro, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or

R²³ and R²⁴ together with the atom to which they are attached form a cyclopropyl group,

R²¹ is selected from groups [21], [22], [22A], [22B], [23], [24], [25] and [26] wherein the atom marked ** is directly connected to B:

R²⁵ and R²⁶ are each independently selected from H, C₁₋₄ alkyl, C₁₋₄ fluoroalkyl or benzyl;

R²⁷ is independently selected from H, C₁₋₄ alkyl, C₁₋₄ fluoroalkyl;

R²⁸ is selected from:

(i) H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or

(ii) the side chain of a natural or unnatural alpha-amino acid;

or R²⁷ and R²⁸ together with the atom to which they are attached form a C₃₋₇ carbocyclic ring;

R²⁹ is selected from H, —N(R³¹)(R³²), or —N⁺(R³¹)(R³²)(R³³)X⁻, or —N(R³¹)C(O)R³⁴ wherein R³¹, R³², and R³³ are independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or R³¹ and R³² together with the nitrogen atom to which they are attached form a 3-8 membered heterocyclic ring,

R³⁴ is H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl,

X⁻ is a pharmaceutically acceptable anion,

R³⁰ and R³⁵ are independently C₁₋₄ alkyl or C₁₋₄ fluoroalkyl.

In a third aspect, the present invention makes available a class of compounds of formula (IIIa) or (IIIb), or a hydrate, solvate, or pharmaceutically acceptable salt thereof:

wherein Z₁, Z₂, and Z₃ are each independently selected from H, F, or Cl; and

R² and -A-R¹ are both H; and

In the case of formula (IIIa):

R⁴¹ and R⁴² are independently H, C₁₋₄ fluoroalkyl or optionally substituted C₁₋₄ alkyl, or

R⁴¹ and R⁴² together with the carbon atom to which they are attached form a 5-8 membered heterocycle, any carbon atom of which is optionally substituted; or

In the case of formula (IIIb):

Q is an oxime of formula ═NHOR⁴³, wherein R⁴³ is

(i) selected from H, C₁₋₄ fluoroalkyl or optionally substituted C₁₋₄ alkyl, or

(ii) -A³⁰⁰-R³⁰⁰ wherein

A³⁰⁰ is a direct bond, —C(O)O*—, —C(R³)(R⁴)O*—, —C(O)O—C(R³)(R⁴)O*—, or —C(R³)(R⁴)O—C(O)O*— wherein the atom marked * is directly connected to R³⁰⁰,

R³ and R⁴ are selected independently from H, fluoro, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or

R³ and R⁴ together with the atom to which they are attached form a cyclopropyl group,

R³⁰⁰ is selected from groups [1], [2], [2A], [2B], [3], [4], [5] or [6] wherein the atom marked ** is directly connected to A³⁰⁰:

R⁵ and R⁶ are each independently selected from H, C₁₋₄ alkyl, C₁₋₄ fluoroalkyl, or benzyl;

R⁷ is independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl;

R⁸ is selected from:

(iii) H, C₁₋₄ alkyl, or C₁₋₄-fluoroalkyl, or

(iv) the side chain of a natural or unnatural alpha-amino acid;

or R⁷ and R⁸ together with the atom to which they are attached form a C₃₋₇ carbocyclic ring;

R⁹ is selected from H, —N(R¹¹)(R¹²), or —N⁺(R¹¹)(R¹²)(R¹³)X⁻, or —N(R¹¹)C(O)R¹⁴ wherein R¹¹, R¹², and R¹³ are independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 3-8 membered heterocyclic ring,

R¹⁴ is H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl

R¹⁰ and R¹⁵ are independently selected from C₁₋₄ alkyl or C₁₋₄ fluoroalkyl,

X⁻ is a pharmaceutically acceptable anion.

In an embodiment R⁴³ is C₁₋₄ alkyl optionally substituted with a phosphate group (—P(O)OR⁶¹R⁶²). In an example of such an embodiment OR⁴³ is —OCH₂P(O)OR⁶¹OR⁶², wherein R⁶¹ and R⁶² are independently H or C₁₋₄ alkyl.

In another embodiment R⁴³ is an amino acid derivative having the structure —C(O)CH(R¹⁰⁰)NH₂ wherein the group R¹⁰⁰ is the side chain of a natural or unnatural amino acid. In an embodiment OR⁴³ is —OC(O)CH(CH(CH₃)₂)NH₂.

Preferably the invention is as set out in the claims.

TERMINOLOGY

As used herein, the term “(C_(a)-C_(b))alkyl” wherein a and b are integers refers to a straight or branched chain alkyl radical having from a to b carbon atoms. Thus when a is 1 and b is 6, for example, the term includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and n-hexyl.

As used herein, the term “(C_(a)-C_(b))fluoroalkyl” has the same meaning as “(C_(a)-C_(b))alkyl” except that one or more of the hydrogen atoms directly connected to the carbon atoms forming the alkyl group is replaced by the corresponding number of fluorine atoms.

As used herein the unqualified term “carbocyclic” refers to a mono-, bi- or tricyclic radical having up to 16 ring atoms, all of which are carbon, and includes aryl and cycloalkyl.

As used herein the unqualified term “cycloalkyl” refers to a monocyclic saturated carbocyclic radical having from 3-8 carbon atoms and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

As used herein the unqualified term “aryl” refers to a mono-, bi- or tri-cyclic carbocyclic aromatic radical, and includes radicals having two monocyclic carbocyclic aromatic rings which are directly linked by a covalent bond. Illustrative of such radicals are phenyl, biphenyl and napthyl.

As used herein the unqualified term “heteroaryl” refers to a mono-, bi- or tri-cyclic aromatic radical containing one or more heteroatoms selected from S, N and O, and includes radicals having two such monocyclic rings, or one such monocyclic ring and one monocyclic aryl ring, which are directly linked by a covalent bond. Illustrative of such radicals are thienyl, benzthienyl, furyl, benzfuryl, pyrrolyl, imidazolyl, benzimidazolyl, thiazolyl, benzthiazolyl, isothiazolyl, benzisothiazolyl, pyrazolyl, oxazolyl, benzoxazolyl, isoxazolyl, benzisoxazolyl, isothiazolyl, triazolyl, benztriazolyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, triazinyl, indolyl and indazolyl.

As used herein the unqualified term “heterocyclyl” or “heterocyclic” includes “heteroaryl” as defined above, and in addition means a mono-, bi- or tri-cyclic non-aromatic radical containing one or more heteroatoms selected from S, N and O, and to groups consisting of a monocyclic non-aromatic radical containing one or more such heteroatoms which is covalently linked to another such radical or to a monocyclic carbocyclic radical. Illustrative of such radicals are pyrrolyl, furanyl, thienyl, piperidinyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, thiadiazolyl, pyrazolyl, pyridinyl, pyrrolidinyl, pyrimidinyl, morpholinyl, piperazinyl, indolyl, morpholinyl, benzfuranyl, pyranyl, isoxazolyl, benzimidazolyl, methylenedioxyphenyl, ethylenedioxyphenyl, maleimido and succinimido groups.

Unless otherwise specified in the context in which it occurs, the term “substituted” as applied to any moiety herein means substituted with up to four compatible substituents, each of which independently may be, for example, (C₁-C₆)alkyl, (C₁-C₆)alkoxy, hydroxy, hydroxy(C₁-C₆)alkyl, mercapto, mercapto(C₁-C₆)alkyl, (C₁-C₆)alkylthio, halo (including fluoro, bromo and chloro), fully or partially fluorinated (C₁-C₃)alkyl, (C₁-C₃)alkoxy or (C₁-C₃)alkylthio such as trifluoromethyl, trifluoromethoxy, and trifluoromethylthio, nitro, nitrile (—CN), oxo, phenyl, phenoxy, monocyclic heteroaryl or heteroaryloxy with 5 or 6 ring atoms, tetrazolyl, —COOR^(A), —COR^(A), —OCOR^(A), —SO₂R^(A), —CONR^(A)R^(B), —SO₂NR^(A)R^(B), —NR^(A)R^(B), OCONR^(A)R^(B), —NR^(B)COR^(A), —NR^(B)COOR^(A), —NR^(B)SO₂OR^(A) or —NR^(A)CONR^(A)R^(B) wherein R^(A) and R^(B) are independently hydrogen or a (C₁-C₆)alkyl group or, in the case where R^(A) and R^(B) are linked to the same N atom, R^(A) and R^(B) taken together with that nitrogen may form a cyclic amino ring, such as a morpholine, piperidinyl or piperazinyl ring. Where the substituent is phenyl, phenoxy or monocyclic heteroaryl or heteroaryloxy with 5 or 6 ring atoms, the phenyl or heteroaryl ring thereof may itself be substituted by any of the above substituents except phenyl, phenoxy, heteroaryl or heteroaryloxy. An “optional substituent” may be one of the foregoing substituent groups.

As used herein the term “salt” includes base addition, acid addition and quaternary salts. Compounds of the invention which are acidic can form salts, including pharmaceutically acceptable salts, with bases such as alkali metal hydroxides, e.g. sodium and potassium hydroxides; alkaline earth metal hydroxides e.g. calcium, barium and magnesium hydroxides; with organic bases e.g. N-methyl-D-glucamine, choline tris(hydroxymethyl)amino-methane, L-arginine, L-lysine, N-ethyl piperidine, dibenzylamine and the like. Those compounds of formula (I), (II), (IIIa) or (IIIb) which are basic can form salts, including pharmaceutically acceptable salts with inorganic acids, e.g. hydrohalic acids such as hydrochloric or hydrobromic acids, sulphuric acid, nitric acid or phosphoric acid and the like, and with organic acids e.g. acetic, tartaric, succinic, fumaric, maleic, malic, salicylic, citric, methanesulphonic, p-toluenesulphonic, benzoic, benzenesunfonic, glutamic, lactic, and mandelic acids and the like.

The formation of specific salt forms can provide compounds of the invention with improved physicochemical properties. For a review on suitable salts, see Handbook of Pharmaceutical Salts: Properties, Selection, and Use by Stahl and Wermuth (Wiley-VCH, Weinheim, Germany, 2002).

The term ‘solvate’ is used herein to describe a molecular complex comprising the compound of the invention and a stoichiometric amount of one or more pharmaceutically acceptable solvent molecules, for example, ethanol. The term ‘hydrate’ is employed when said solvent is water.

Compounds with which the invention is concerned which may exist in one or more stereoisomeric form, because of the presence of asymmetric atoms or rotational restrictions, can exist as a number of stereoisomers with R or S stereochemistry at each chiral centre or as atropisomers with R or S stereochemistry at each chiral axis. The invention includes all such enantiomers and diastereoisomers and mixtures thereof. In particular, the carbon atom to which the groups R⁷ and R⁷ are attached may be in either the R or the S configuration.

The compounds of the invention include compounds of formula (I), (II), (IIIa) or (IIIb) as hereinbefore defined, including all polymorphs and crystal habits thereof, prodrugs and isomers thereof (including optical, geometric and tautomeric isomers) as hereinafter defined and isotopically-labeled compounds of formula (I), (II), (IIIa) or (IIIb).

Also included within the scope of the invention are metabolites of compounds of formula (I), (II), (IIIa) or (IIIb), that is, compounds formed in vivo upon administration of the drug. Some examples of metabolites include:

-   (i) where the compound of formula I contains a methyl group, an     hydroxymethyl derivative thereof (—CH₃->—CH₂OH): -   (ii) where the compound of formula I contains an alkoxy group, an     hydroxy derivative thereof (—OR->—OH); -   (iii) where the compound of formula I contains a tertiary amino     group, a secondary amino derivative thereof (e.g.     —NR^(1A)R_(2A)->NHR^(1A) or —NHR^(2A)); -   (iv) where the compound of formula I contains a secondary amino     group, a primary derivative thereof (—NHR^(1A)->—NH₂); -   (v) where the compound of formula I contains a phenyl moiety, a     phenol derivative thereof (-Ph->-PhOH); and -   (vi) where the compound of formula I contains an amide group, a     carboxylic acid derivative thereof (—CONH₂->COOH).

For use in accordance with the invention, the following structural characteristics are currently contemplated, in any compatible combination, in the compounds of formula (I):

The groups Z₁, Z₂, and Z₃ are each independently selected from H, F, or Cl. In an embodiment Z₁ is Cl, Z₂ is F, and Z₃ is H. In another embodiment Z₁ is Cl, Z₂ and Z₃ are H. In another embodiment Z₁ is H, Z₂ is F, and Z₃ is H. In another embodiment Z₁ is F, Z₂ is H, and Z₃ is F. The above definitions of Z₁, Z₂, and Z₃ is H are applicable to compounds of formula (I), (II), (IIIa), and (IIIb). As an illustration, the preferred definition of Z₁, Z₂, and Z₃ applied to the compounds of formula (I) is as follows:

In a preferred embodiment Z₁ is Cl, Z₂ is F or H, and Z₃ is H.

The group Q is an oxygen atom

The group R² is a hydrogen atom

The group A is a direct bond, —C(O)O*—, —C(R³)(R⁴)O*—, —C(O)O—C(R³)(R⁴)O*—, or —C(R³)(R⁴)O—C(O)O*— wherein the atom marked * is directly connected to R¹.

The groups R³ and R⁴ are selected independently from H, fluoro, C₁₋₄ alkyl such as methyl, ethyl, propyl or isopropyl, or C₁₋₄ fluoroalkyl such as trifluoromethyl, or R³ and R⁴ together with the atom to which they are attached form a cyclopropyl group,

In an embodiment A is a direct bond. In another embodiment A is —CH₂O*—, or —CH(CH₃)O*—, or C(CH₃)₂O*—.

The group R¹ is selected from groups [1], [2], [2A], [2B], [3], [4], [5] or [6] wherein the atom marked ** is directly connected to A:

The groups R⁵ and R⁶ are each independently selected from H, C₁₋₄ alkyl such as methyl, ethyl, propyl or isopropyl, C₁₋₄ fluoroalkyl such as trifluoromethyl, or benzyl. In an embodiment R⁵ and R⁶ are hydrogen.

The group R⁷ is independently selected from H, C₁₋₄ alkyl such as methyl, ethyl, propyl or isopropyl, or C₁₋₄ fluoroalkyl such as trifluoromethyl. In another embodiment R⁷ and R⁸ are both hydrogen, or R⁷ is hydrogen and R⁸ is methyl, or both R⁷ and R⁸ are methyl. In an embodiment R⁷, R⁸ and R⁹ are hydrogen. In an embodiment R⁷ is hydrogen.

The group R⁸ is selected from:

-   -   (i) H, C₁₋₄ alkyl such as methyl, ethyl, propyl, or isopropyl,         or C₁₋₄-fluoroalkyl such as trifluoromethyl, or     -   (ii) the side chain of a natural or unnatural alpha-amino acid;

or R⁷ and R⁸ together with the atom to which they are attached form a C₃₋₇ carbocyclic ring such as cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl;

The term “side chain of a natural or non-natural alpha-amino acid” refers to the group R¹⁰⁰ in a natural or non-natural amino acid of formula NH₂—CH(R¹⁰⁰)—CO₂H.

In an embodiment the group -AR¹ is selected from the following groups wherein the atom marked ** is directly connected to the oxygen atom of the parent drug:

Examples of side chains of natural alpha amino acids include those of alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, histidine, 5-hydroxylysine, 4-hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, α-aminoadipic acid, α-amino-n-butyric acid, 3,4-dihydroxyphenylalanine, homoserine, α-methylserine, ornithine, pipecolic acid, and thyroxine.

Natural alpha-amino acids which contain functional substituents, for example amino, carboxyl, hydroxy, mercapto, guanidyl, imidazolyl, or indolyl groups in their characteristic side chains include arginine, lysine, glutamic acid, aspartic acid, tryptophan, histidine, serine, threonine, tyrosine, and cysteine. When R⁸ in the compounds of the invention is one of those side chains, the functional substituent may optionally be protected.

The term “protected” when used in relation to a functional substituent in a side chain of a natural alpha-amino acid means a derivative of such a substituent which is substantially non-functional. For example, carboxyl groups may be esterified (for example as a C₁-C₆ alkyl ester), amino groups may be converted to amides (for example as a NHCOC₁-C₆ alkyl amide) or carbamates (for example as an NHC(═O)OC₁-C₆ alkyl or NHC(═O)OCH₂Ph carbamate), hydroxyl groups may be converted to ethers (for example an OC₁-C₆ alkyl or a O(C₁-C₆ alkyl)phenyl ether) or esters (for example a OC(═O)C₁-C₆ alkyl ester) and thiol groups may be converted to thioethers (for example a tert-butyl or benzyl thioether) or thioesters (for example a SC(═O)C₁-C₆ alkyl thioester).

Examples of side chains of non-natural alpha amino acids include: an optional substituent, C₁-C₆ alkyl, phenyl, 2, -3-, or 4-hydroxyphenyl, 2, -3-, or 4-methoxyphenyl, 2, -3-, or 4-pyridylmethyl, benzyl, phenylethyl, 2-, 3-, or 4-hydroxybenzyl, 2, -3-, or 4-benzyloxybenzyl, 2, -3-, or 4-C₁-C₆ alkoxybenzyl, and benzyloxy(C₁-C₆alkyl)-groups, wherein any of the foregoing non-natural amino acid side chains is optionally substituted in the alkyl, phenyl or pyridyl group; or

groups -[Alk]_(n)R₅₀ where Alk is a (C₁-C₆)alkyl or (C₂-C₆)alkenyl group optionally interrupted by one or more —O—, or —S— atoms or —N(R₅₁)— groups [where R₅₁ is a hydrogen atom or a (C₁-C₆)alkyl group], n is 0 or 1, and R₅₀ is an optionally substituted cycloalkyl or cycloalkenyl group; or

a heterocyclic(C₁-C₆)alkyl group, either being unsubstituted or mono- or di-substituted in the heterocyclic ring with halo, nitro, carboxy, (C₁-C₆)alkoxy, cyano, (C₁-C₆)alkanoyl, trifluoromethyl (C₁-C₆)alkyl, hydroxy, formyl, amino, (C₁-C₆)alkylamino, di-(C₁-C₆)alkylamino, mercapto, (C₁-C₆)alkylthio, hydroxy(C₁-C₆)alkyl, mercapto(C₁-C₆)alkyl or (C₁-C₆)alkylphenylmethyl; and

The group R⁹ is selected from H, —N(R¹¹)(R¹²) such as —NH₂, NH(CH₃), —NH(CH₃)₂, or —N⁺(R¹¹)(R¹²)(R¹³)X⁻ such as —N⁺(CH₃)₃X⁻, or —N(R¹¹)C(O)R¹⁴

wherein R¹¹, R¹², and R¹³ are independently selected from H, C₁₋₄ alkyl such as methyl, ethyl, propyl or isopropyl, or C₁₋₄ fluoroalkyl such as trifluoromethyl, or R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 3-8 membered heterocyclic ring such as pyrrolidine, piperidine, piperazine, morpholine or homomorpholine. In an embodiment R¹¹ and R¹² are both methyl.

R¹⁴ is H, C₁₋₄ alkyl such as methyl, ethyl, propyl or isopropyl, or C₁₋₄ fluoroalkyl such as trifluoromethyl

R¹⁰ and R¹⁵ are independently selected from C₁₋₄ alkyl or C₁₋₄ fluoroalkyl.

The counterion X⁻ is a pharmaceutically acceptable anion such as chloride, or any other anion fromed by removal of one or more protons from an inorganic acid, e.g. hydrohalic acids such as hydrochloric or hydrobromic acids, sulphuric acid, nitric acid or phosphoric acid and the like, or from an organic acids e.g. acetic, tartaric, succinic, fumaric, maleic, malic, salicylic, citric, methanesulphonic, p-toluenesulphonic, benzoic, benzenesunfonic, glutamic, lactic, and mandelic acids and the like.

Specific compounds of the invention include those of the Examples herein.

It will be understood that the compounds of formula (I), (II), (IIIa) or (IIIb) may be further modified by adding one or more of the prodrug groups Q, -AR¹ or R². For example the compounds of formula (I) or (ii) may be modified by exchanging the oxygen atom Q for a prodrug Q group as defined in (IIIa) or (IIIb). Alternatively, the compounds of formula (I) could be modified by replacing the hydrogen atom R2 by the prodrug group R2 as defined in formula (II), and vice versa.

The present invention makes available a pharmaceutical composition comprising a compound of formula (I), (II), (IIIa) or (IIIb) together with one or more pharmaceutically acceptable carriers and/or excipients.

The present invention makes available a compound of formula (I), (II), (IIIa) or (IIIb) for use in medicine.

In an embodiment the inventions encompasses the use of a compound of formula (I), (II), (IIIa) or (IIIb) treatment of a disease or medical condition which benefits from inhibition of gap junction activity. Inhibition of gap junction activity may be achieved by blocking the gap junction as a whole or by blocking one or more hemichannels.

In an embodiment the inventions encompasses a method of treatment of a disease or medical condition which benefits from inhibition of gap junction activity, comprising administering to a subject suffering from such disease or condition and effective amount of a compound of formula (I), (II), (IIIa) or (IIIb).

In an embodiment the disease or condition which benefits from inhibition of gap junction activity is selected from among migraine, aura with or without migraine, epilepsy, non-epileptic seizures, cerebrovascular accidents including stroke, intracranial haemorrhage (including traumatic brain injury, epidural hematoma, subdural hematoma and subarachnoid haemorrhage), and intra-cerebral haemorrhage, spinal cord vascular accidents arising from trauma, epidural hematoma, subdural hematoma or subarachnoid haemorrhage, pain including pain arising from hyperalgesia caused by damage to sensory neurons (i.e. neuropathic pain including but not limited to diabetic neuropathy, polyneuropathy, cancer pain, fibromyalgia, myofascial pain, post herpetic neuralgia, spinal stenosis, HIV pain, post-operative pain, post-trauma pain) or inflammation (including pain associated with osteoarthritis, rheumatoid arthritis, sciatica/radiculopathy, pancreatitis, tendonitis), neurodegenerative disease (including but not limited to Alzheimer's Disease, Parkinson's Disease, Huntington's Disease and Amyotrophic Lateral Sclerosis) and cardiovascular disease including myocardial infarction, coronary revascularization or angina.

It will be understood that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination and the severity of the particular disease undergoing treatment. Optimum dose levels and frequency of dosing will be determined by clinical trial, as is required in the pharmaceutical art. However, for administration to human patients, the total daily dose of the compounds of the invention may typically be in the range 1 mg to 1000 mg depending, of course, on the mode of administration. For example, oral administration may require a total daily dose of from 10 mg to 1000 mg, while an intravenous dose may only require from 1 mg to 500 mg. The total daily dose may be administered in single or divided doses and may, at the physician's discretion, fall outside of the typical range given herein. These dosages are based on an average human subject having a weight of about 60 kg to 100 kg. The physician will readily be able to determine doses for subjects whose weight falls outside this range, such as infants and the elderly, and especially obese patients.

The compounds with which the invention is concerned may be prepared for administration by any route consistent with their pharmacokinetic properties. Suitable routes for administration include oral, intravenous, buccal, intranasal, inhalation, rectal, and intradermal. The orally administrable compositions may be in the form of tablets, capsules, powders, granules, lozenges, liquid or gel preparations, such as oral, topical, or sterile parenteral solutions or suspensions. Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrrolidone; fillers for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricant, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, glucose syrup, gelatin hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters such as glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.

The pro-drug may also be administered parenterally in a sterile medium. Depending on the vehicle and concentration used, the drug can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as local anaesthetic, preservative and buffering agents can be dissolved in the vehicle. The person skilled in the art is aware of many excipients useful for IV formulation.

Preparation of Compounds of the Invention

The compounds of formula (I) above may be prepared by, or in analogy with, conventional methods. The preparation of intermediates and compounds according to the Examples of the present invention may in particular be illuminated by the following Schemes. Definitions of variables in the structures in Schemes herein are commensurate with those of corresponding positions in the formulas delineated herein.

wherein A, Q, Z₁, Z₂, Z₃, R¹ and R² are as defined in formula (I);

Compounds of general formula (I) can easily be prepared from the alcohols of general formula (IV) by either using the alcohol directly or pre-forming the alkoxide using a suitable base/reagent (e.g. NaH) and coupling to a suitably activated A-R or R group (or protected A-R or R group). Activated A-R or R group functionalities typically used for the formation of phosphates, esters, carbonates and carbamates include, but not limited to, phosphoryl chlorides, acid chlorides, activated carboxylic acids, chloroformates, activated carbonates and isocyanates. The formation of (la) from (IV) using dimethylaminoacetyl chloride as an activated R group is representative of this approach. When the compound of general formula (I) has an A group defined as —C(R³)(R⁴)O*— or C(R³)(R⁴)OC(O)O*— these may be prepared from compounds of general formula (IV) using an appropriate alkylating agent which may include, but not limited to, alkylchlorides, alkylbromides, alkyliodides, mesylates and tosylates. The formation of (Ib) from (IV) using NaH to form the sodium alkoxide of (IV) followed by coupling with bromomethyl acetate as an activated A-R group is representative of this approach.

wherein A, Q, Z₁, Z₂, Z₃, R¹ and R² are as defined in formula (I);

P¹ is a suitable protecting group or functionality that can be readily chemically modified/utilised to append R¹.

Alternatively, compounds of general formula (I) can easily be prepared in a more step wise manner from the alcohol of general formula (IV) by using either the alcohol directly or pre-forming the alkoxide using a suitable base/reagent (e.g. NaH) and coupling to a suitably activated A-P¹ group. When the compound of general formula (I) has an A group defined as —C(R³)(R⁴)O*— or C(R³)(R⁴)OC(O)O*— these may be prepared using activated forms of A-P¹ including, but not limited to, alkylchlorides, alkylbromides, alkyliodides, mesylates and tosylates. When the compound of general formula (I) has an A group defined as —C(O)O*— or C(O)OC(R³)(R⁴)O*— these may be prepared using activated forms of A-P¹ including, but not limited to, chloroformates and activated carbonates. Then using methods known to those skilled in the art the intermediates of general formula (V) can be chemically modified to provide functionality that facilitates the final coupling step to afford compounds of general formula (I). The formation of (Ic) from (IV) via the methylsulfanyl methoxy intermediate (Va) is representative of this approach.

The synthesis of Tonabersat, and other structurally related compounds, is disclosed in WO 95/34545. The present invention encompasses compounds prepared by applying the pro-drug groups -AR¹, R² and Q taught herein to the specific Examples disclosed in WO 95/34545. The methods proposed for the synthesis of compounds of general formula (I) are known to those skilled in the art, for example in Rautio et al., Nature Reviews Drug Discovery, 7, 255-270, 2008.

Optionally, a compound of formula (I) can also be transformed into another compound of formula (I) in one or more synthetic steps.

The following abbreviations have been used:

Boc tertiary-butyloxycarbonyl

d day(s)

DCM dichloromethane

DIPEA diisopropylethylamine

DMAP 4-dimethylaminopyridine

DME dimethoxyethane

DMF dimethylformamide

EDC 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide

ES+ electrospray ionization

EtOAc ethyl acetate

Et₂O diethyl ether

Et₃N triethylamine

EtOH ethanol

h hour(s)

HOBt Hydroxybenzotriazole

HPLC High Performance Liquid Chromatography

HRMS High-Resolution Mass Spectrometry

IMS Industrial methylated spirit

LCMS Liquid Chromatography Mass Spectrometry

Leu Leucine

M molar

MeCN acetonitrile

MeOH methanol

MTBE methyl tertiary-butyl ether

[MH]⁺ protonated molecular ion

min minute(s)

MS Mass Spectrometry

Rt retention time

TFA trifluoroacetic acid

THF tetrahydrofuran

EXAMPLES AND INTERMEDIATE COMPOUNDS Experimental Methods

Reactions were conducted at room temperature unless otherwise specified. Preparative chromatography was performed using a Flash Master Personal system equipped with Isolute Flash II silica columns or using a CombiFlash Companion system equipped with GraceResolv silica column. The purest fractions were collected, concentrated and dried under vacuum. Compounds were typically dried in a vacuum oven at 40° C. prior to purity analysis. Compound analysis was performed by HPLC/LCMS using an Agilent 1100 HPLC system/Waters ZQ mass spectrometer connected to an Agilent 1100 HPLC system with a Phenomenex Synergi, RP-Hydro column (150×4.6 mm, 4 μm, 1.5 mL per min, 30° C., gradient 5-100% MeCN (+0.085% TFA) in water (+0.1% TFA) over 7 min, 200-300 nm). The compounds prepared were named using IUPAC nomenclature.

Intermediate 1 N-[(3S,4S)-6-acetyl-2,2-dimethyl-3-[(methylsulfanyl)methoxy]-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (1.00 g, 2.55 mmol) was dissolved in DME (10 mL) and added to a suspension of sodium hydride (60% dispersion in oil, 112 mg, 2.81 mmol) in DME (10 mL). The reaction mixture was stirred for 10 min then sodium iodide (421 mg, 2.81 mmol) was added followed by chloromethyl methyl sulfide (232 μL, 2.81 mmol). The reaction mixture was stirred for 18 h then quenched with saturated aqueous ammonium carbonate solution (5 mL), diluted with EtOAc (50 mL), washed with water (3×25 mL), dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with a gradient of EtOAc in heptane to give the title compound (405 mg, 35.1%) as a white solid. LCMS (ES⁺): 452.1 [MH]⁺. HPLC: Rt 6.36 min, 86.2% purity.

Intermediate 2 2-{[(tert-Butoxy)carbonyl](propyl)amino}acetic acid

Glyoxylic acid monohydrate (4.67 g, 5.08 mmol) and 1-propylamine (1.50 g, 25.4 mmol) were dissolved in DCM (100 mL) and the reaction mixture was stirred for 18 h and concentrated in vacuo. 1M aq HCl (125 mL, 125 mmol) was added and the reaction mixture was heated under reflux overnight, concentrated in vacuo and crystallised from i-PrOH/Et₂O to give a white solid. The 2-(propylamino)acetic acid hydrochloride intermediate (2.49 g, 16.2 mmol), di-tert-butyl dicarbonate (8.84 g, 40.5 mmol) and Et₃N (11.3 mL, 81.1 mmol) were dissolved in water (65 mL) and stirred for 3d. The reaction mixture was washed with hexane and the aqueous fraction was acidified with 2M aq HCl and extracted into EtOAc, washed with brine, dried (MgSO₄) and concentrated in vacuo to give the title compound (3.40 g, 61.9%) as a colourless oil. LCMS (ES⁻): 216.1 [MH]⁻.

Example 1 {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}phosphonic acid

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (2.00 g, 5.10 mmol) was dissolved in methylethyl ketone (50 mL). Pyridine (1.62 mL, 20.4 mmol) and POCl₃ (1.50 mL, 16.3 mmol) were added and the reaction mixture was stirred for 16 h. A precipitate was removed by filtration, washed with methylethyl ketone (50 mL) and 2M aq HCl (10 mL) added to the combined methylethyl ketone phases. The reaction mixture was heated at 65° C. for 1 h. The organic phase was washed with brine (10 mL), dried (MgSO₄) and concentrated in vacuo. The residue was dissolved in EtOAc (50 mL) and stirred for 30 min. The resulting precipitate was collected by filtration, washed with EtOAc (20 mL) and the solid dried in vacuo to give the title compound (1.67 g, 69.3%) as a white solid. LCMS (ES⁺): 471.9 [MH]⁺. HPLC: Rt 4.84 min, 100% purity.

Example 2 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(dimethylamino)acetate hydrochloride

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (100 mg, 0.26 mmol) was dissolved in THF (10 mL). Et₃N (78.3 μL, 0.56 mmol), DMAP (3 mg, catalytic) and dimethylaminoacetyl chloride hydrochloride (40.3 mg, 0.26 mmol) were added and the reaction mixture was stirred for 16 h. Further Et₃N (78.3 μL, 0.56 mmol) and dimethylaminoacetyl chloride hydrochloride (40.3 mg, 0.26 mmol) were added and the reaction mixture was stirred for 1 h. Further Et₃N (157 μL, 1.12 mmol) and dimethylaminoacetyl chloride hydrochloride (80.6 mg, 0.52 mmol) were added and the reaction mixture was stirred for 1 h. The reaction mixture was filtered, washed with THF (30 mL) and the filtrates diluted with EtOAc (70 mL). The organic phase was washed with saturated aqueous NaHCO₃ (2×30 mL), dried (MgSO₄) and concentrated in vacuo. The residue was dissolved in Et₂O (10 mL). 2M HCl in Et₂O (2 mL) was added and the resulting precipitate was collected by filtration, washed with Et₂O (10 mL) and dried in vacuo to give the title compound (50.0 mg, 41.1%) as an off-white solid. LCMS (ES⁺): 476.9 [MH]⁺. HPLC: Rt 5.14 min, 97.9% purity.

Example 3 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl acetate

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (200 mg, 0.51 mmol) was slurried in toluene (2.0 mL) with acetic anhydride (50 μL, 0.51 mmol), N-hydroxysuccinimide (18 mg, 0.15 mmol) and 4-dimethylaminopyridine (6 mg, 0.05 mmol). The reaction mixture was heated to 80° C. for 195 min to give a colourless solution and then cooled to ambient temperature overnight. The reaction mixture was diluted with toluene (2 mL) and washed with 10% aqueous citric acid (4 mL) and water (4 mL). The toluene phase was evaporated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with heptane/ethyl acetate mixtures. The product was crystallised from toluene (1 mL)/heptane (3 mL) overnight. The solid was collected by filtration, washed with heptane (2 mL) and dried in vacuo at 40° C. overnight to give the title compound (88.1 mg, 39.8%) as a white solid. LCMS (ES⁺): 434.0 [MH]⁺. HPLC: Rt 6.32 min, 97.8% purity.

Example 4 {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl acetate

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (229 mg, 0.58 mmol) was stirred in DMF (4.0 mL) with NaH (60% dispersion, 45 mg, 0.68 mmol) for 20 min. Bromomethyl acetate (69 μL, 0.70 mmol) was added and the mixture stirred at room temperature for 90 min. The reaction mixture was quenched with water (8 mL) and extracted with EtOAc (2×5 mL). The combined organic extracts were washed with water (5 mL) and the organic phase evaporated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with 4:1 heptane:EtOAc to give the title compound (88 mg; 32.5%) as a white solid. LCMS (ES⁺): 464.0 [MH]⁺. HPLC: Rt 6.52 min, 97.3% purity.

Example 5 {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl 2-(dimethylamino)acetate

Intermediate 1 (261 mg, 0.58 mmol) was dissolved in DCM (7 mL) and treated with sulfuryl chloride (51.5 μL, 0.64 mmol). The reaction mixture was stirred for 10 min. N,N-Dimethylglycine (298 mg, 2.89 mmol) and DIPEA (1.00 mL, 5.78 mmol) were dissolved in DCM (3 mL) and added to the reaction mixture. After 30 min the reaction mixture was poured into 1M aqueous Na₂CO₃ (50 mL) and extracted with DCM (2×50 mL). The combined organic layers were dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with a gradient of EtOAc in heptane. The pure fractions were combined and dried in vacuo overnight to give the title compound (114 mg, 38.9%) as a white solid. LCMS (ES⁺): 507.1 [MH]⁺. HPLC: Rt 4.99 min, 98.3% purity.

Example 6 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-aminoacetate hydrochloride

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (400 mg, 1.02 mmol) was dissolved in DCM (8 mL) at room temperature. Boc-Gly-OSu (full name: 2,5-dioxopyrrolidin-1-yl 2-{[(tert-butoxy)carbonyl]amino}acetate) (556 mg, 2.04 mmol), DIPEA (391 L, 2.25 mmol) and DMAP (12 mg, 0.10 mmol) were added. The reaction mixture was stirred overnight. The DCM was evaporated in vacuo and the residue suspended between EtOAc (15 mL) and 10% aqueous citric acid solution (10 mL). The organic phase was washed with water (10 mL) and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with heptane/EtOAc mixtures. The (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-{[(tert-butoxy)carbonyl]amino}acetate intermediate was dissolved in 4M HCl in dioxane (4 mL) and stirred at room temperature for 90 min. The solvents were removed in vacuo and the residue partitioned between EtOAc (10 mL) and saturated aqueous Na₂CO₃ solution (5 mL). The aqueous layer was extracted with EtOAc (10 mL) and the combined organic phases concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with heptane/ethyl acetate mixtures. To each pure fraction was added 1.25M HCl in EtOH (200 μL). The pure fractions were combined and dried in vacuo to give the title compound (93 mg, 18.8%) as a white foam. LCMS (ES⁺): 449.0 [MH]⁺. HPLC: Rt 4.95 min, 96.9% purity.

Example 7 (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(methylamino)acetate hydrochloride

N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (200 mg, 0.51 mmol) was dissolved in THF (4 mL) at room temperature. Boc-Sar-OSu (full name: tert-butyl N-{2-[(2,5-dioxopyrrolidin-1-yl)oxy]-2-hydroxyethyl}-N-methylcarbamate) (292 mg, 1.02 mmol), DIPEA (196 μL, 1.12 mmol) and DMAP (6 mg, 0.05 mmol) were added and the reaction mixture was stirred overnight at 70° C. The THF was evaporated in vacuo and the residue suspended between EtOAc (10 mL) and 10% aqueous citric acid solution (5 mL). The organic phase was washed with water (10 mL) and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with heptane/EtOAc mixtures. The (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-{[(tert-butoxy)carbonyl](methyl)amino}acetate intermediate was dissolved in 4M HCl in dioxane (2 mL) and stirred at room temperature for 1 h. The solvents were removed in vacuo. The residue was triturated in EtOAc/MTBE mixture and then stirred with ice bath cooling for 1 h. The solid was collected by filtration, washed with MTBE (2 mL) and dried in vacuo at 50° C. to give the title compound (110 mg, 43.2%) as a white solid. LCMS (ES⁺): 463.1[MH]⁺. HPLC: Rt 5.06 min, 98.6% purity.

Example 8 ({[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methoxy)phosphonic acid diamine

Intermediate 1 (600 mg, 1.33 mmol) was dissolved in THF (12 mL) and treated with phosphoric acid (85%, 911 mg, 9.29 mmol) and powdered 4 Å molecular sieves (1.80 g) at room temperature. The reaction mixture was cooled in an ice bath and N-iodosuccinimide (478 mg; 2.12 mmol) added. The reaction mixture was stirred in an ice bath for 5 min. After overnight at room temperature the reaction mixture was diluted with EtOAc (30 mL). The molecular sieves were removed by filtration and washed with EtOAc (10 mL). The combined organic filtrates were washed with 5% aqueous sodium thiosulfate solution (25 mL). The product was extracted into 10% aqueous sodium carbonate solution (30 mL). The aqueous phase was separated, adjusted to pH1-2 with 2N HCl in ice and the product extracted into EtOAc (15 mL). The organic phase was washed with water (3×10 mL) until pH 4 and then concentrated in vacuo. The residue was partitioned between EtOAc (20 mL) and 5% aqueous sodium carbonate solution (20 mL). The aqueous phase was separated, adjusted to pH 1 with 2N HCl in ice, loaded onto a preconditioned column of Amberlite XAD-4 resin (5 g) and the product eluted with water/MeCN mixtures. The solvents were removed in vacuo and the residue triturated in EtOAc/MTBE mixture. The solid was collected by filtration, washed with MTBE and dried. The solid was partitioned between water (10 mL) and EtOAc (5 mL). 7N Ammonia in MeOH (1 mL) was added. The aqueous phase was separated, concentrated in vacuo, triturated with EtOAc (2×5 mL) and dried in vacuo at 40° C. to give the title compound (44 mg, 6.18%) as a white solid. HPLC: Rt 4.88 min, 98.5% purity.

Example 9 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl (2S)-2-amino-4-methylpentanoate hydrochloride

Boc-Leu-OH (full name: (2S)-2-{[(tert-butoxy)carbonyl]amino}-4-methylpentanoic acid) (555 mg, 2.40 mmol), HOBt hydrate (429 mg, 2.80 mmol), EDC.HCl (537 mg, 2.80 mmol) and DMAP (733 mg, 6.00 mmol) were dissolved in DCM (15 mL) and the reaction mixture was stirred for 15 min. N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (784 mg, 2.00 mmol) was added and the reaction mixture was stirred for 4d, diluted with EtOAc, washed with 10% aq citric acid, 10% aq NaHCO₃ and brine, dried (MgSO₄) and concentrated in vacuo. This procedure was repeated on the same scale and the combined reaction products were purified by column chromatography on normal phase silica eluting with hexane/EtOAc mixtures. The (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl (2S)-2-{[(tert-butoxy)carbonyl]amino}-4-methylpentanoate intermediate (520 mg, 0.86 mmol) was dissolved in DCM (10 mL) and 4N HCl in dioxane (4.3 mL) was added. The reaction mixture was stirred until completion, diluted with EtOAc, washed with 1M aq NaOH, water and brine, dried (MgSO₄) and concentrated in vacuo. The residue was dissolved in Et₂O and acidified with 2M HCl in Et₂O, and the resulting precipitate was collected by filtration, washed with Et₂O and dried in vacuo at 40° C. to give the title compound (273 mg, 12.9%) as a white solid. LCMS (ES⁺): 505.1 [MH]⁺. HPLC: Rt 5.57 min, 99.2% purity.

Example 10 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(propylamino)acetate hydrochloride

Intermediate 2 (478 mg, 2.20 mmol), HOBt hydrate (429 mg, 2.80 mmol), EDC.HCl (537 mg, 2.80 mmol) and DMAP (733 mg, 6.00 mmol) were dissolved in DCM (15 mL) and the reaction mixture was stirred for 15 min. N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (784 mg, 2.00 mmol) was added and the reaction mixture was stirred for 24 h, diluted with EtOAc, washed with 1M aq HCl, 10% aq NaHCO₃ and brine, dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with hexane/EtOAc 3:1. The (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-{[(tert-butoxy)carbonyl](propyl)amino}acetate intermediate (360 mg, 0.61 mmol) was dissolved in DCM (6 mL) and 4N HCl in dioxane (3 mL) was added. The reaction mixture was stirred until completion, diluted with EtOAc, washed with 1M aq NaOH, water and brine, dried (MgSO₄) and concentrated in vacuo. The residue was dissolved in Et₂O and acidified with 2M HCl in Et₂O, and the resulting precipitate was collected by filtration, washed with Et₂O and dried in vacuo at 40° C. to give the title compound (261 mg, 25.9%) as a white solid. LCMS (ES⁺): 491.1 [MH]⁺. HPLC: Rt 5.35 min, 98.7% purity.

Example 11 (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-[(propan-2-yl)amino]acetate hydrochloride

N-Boc-N-isopropylamino-acetic acid (520 mg, 2.39 mmol), HOBt hydrate (441 mg, 2.88 mmol), EDC.HCl (552 mg, 2.88 mmol) and DMAP (733 mg, 6.00 mmol) were dissolved in DCM (10 ml) and the reaction mixture was stirred for 30 min. N-[(3S,4S)-6-Acetyl-3-hydroxy-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-4-yl]-3-chloro-4-fluorobenzamide (784 mg, 2.00 mmol) was added and the reaction mixture was stirred for 20 h and concentrated in vacuo. The residue was purified by column chromatography on normal phase silica eluting with hexane/EtOAc 3:1. The (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-{[(tert-butoxy)carbonyl](propan-2-yl)amino}acetate intermediate (820 mg, 1.39 mmol) was dissolved in MeOH (3 mL) and 4N HCl in dioxane (20 mL) was added. The reaction mixture was stirred for 2 h and concentrated in vacuo. The residue was suspended in diisopropyl ether (50 mL) and EtOAc (1 mL), stirred overnight and collected by filtration. The residue was partitioned between aq NaHCO₃ (20 mL) and DCM (20 mL) and the aqueous fraction was extracted with DCM (2×20 mL). The combined organic fractions were concentrated in vacuo and the residue was purified by normal phase silica eluting with hexane/EtOAc 1:2. The residue was suspended in Et₂O (6 mL) and 2M HCl in Et₂O (2 mL), stirred for 1 h and the precipitate was collected by filtration and washed with Et₂O (2×2 mL) to give the title compound (451 mg, 43.2% in two batches) as a white solid. LCMS (ES⁺): 491.1 [MH]⁺. HPLC: Rt 5.23-5.24 min, 99.5-100% purity.

Preparation of Compounds of Formula (II)

wherein Q, Z₁, Z₂, Z₃ and R² are as defined in the section entitled “detailed description of the invention” and P² is a suitable protecting group.

Compounds of general formula (IIa) can easily be prepared from the alcohols of general formula (IVa) by protecting the hydroxyl functionality with a suitable protecting group P² to give compounds of general formula (VI) and then coupling the prodrug functionality onto the amide nitrogen atom in one or more steps using synthetic strategies analogous to those used for the synthesis of compounds of general formula (I). The final step is to remove the protecting group P² to give compounds of general formula (IIa).

Preparation of Compounds of Formula (IIIa) and (IIIb)

wherein A, Z₁, Z₂, Z₃, R¹ and R² are as defined in the section entitled “detailed description of the invention”

Compounds of general formula (IIIa) can easily be prepared from the ketones of general formula (Id) by either using an alcohol or diol in the presence of an acid and removal of the water generated to prepare acyclic or cyclic ketals respectively. Such methods proposed for the synthesis of compounds of general formula (IIIa) are known to those skilled in the art, for example in T. W. Greene & P. G. M. Wuts, Protective Groups in Organic Synthesis (2nd edition) J. Wiley & Sons, 1991 and P. J. Kocienski, Protecting Groups, Georg Thieme Verlag, 1994.

wherein A, Q, Z₁, Z₂, Z₃, R¹, R², and R⁴³ are as defined in the section entitled “detailed description of the invention”

Compounds of general formula (IIIb) can easily be prepared from the ketones of general formula (I) where Q=O by using the appropriate hydroxylamine and removal of the water generated to prepare the ketoxime. Such methods proposed for the synthesis of compounds of general formula (IIIb) are known to those skilled in the art, for example in T. W. Greene & P. G. M. Wuts, Protective Groups in Organic Synthesis (2nd edition) J. Wiley & Sons, 1991

Biological Rational

Without wishing to be bound by theory, the general mode of action of the claimed pro-drugs is as follows. For IV administration the high solubility conferred by the solubilising pro-moiety to the parent Tonabersat-like drug is expected to allow a rapid bolus injection whereupon the pro-drug will be quickly cleaved by in vivo esterases/phosphatases to reveal the parent drug. For PO administration the preferred mode of action is where the solubilising pro-drug is predominantly cleaved in the gut by esterases/phosphatases prior to absorption of the parent drug into the systemic circulation.

Pharmacokinetics

Example prodrugs were dosed either intravenously or orally to fasted male Sprague Dawley rats. The rats underwent surgery for jugular vein cannulation 48 hrs prior to dosing. Following dosing, 0.25 mL blood samples were taken via the cannulae at 0, 5, 10, 20, 30, 45, 60, 120, 240 & 360 minutes in EDTA coated tubes. Tubes were spun at 13,000 rpm for 4 minutes and 100 ul of supernatant taken immediately and stored at −80° C. prior to analysis. Plasma samples were analysed by LC-MS/MS following extraction by protein precipitation, and levels of parent prodrug and tonabersat were measured by MRM (Multiple Reaction Monitoring) analysis against an extracted calibration curve of plasma samples spiked with the Example prodrug and tonabersat.

Example 2 was dosed according to this protocol at 0.95 mg/kg IV. Plasma levels of Example 2 were found to decline from 730 ng/mL at 5 min to <5 ng/mL at 6 hrs. Plasma levels of tonabersat were determined to be 130 ng/mL at 5 min and 115 ng/mL at 6 hrs clearly showing conversion of the prodrug to tonabersat over this timecourse following intravenous dosing.

Example 2 was dosed according to this protocol at 6.10 mg/kg PO. Plasma levels of Example 2 were found to decline from 38 ng/mL at 5 min to <5 ng/mL at 6 hrs. Plasma levels of tonabersat were determined to be 63 ng/mL at 5 min and 900 ng/mL at 6 hrs clearly showing conversion of the prodrug to tonabersat over this timecourse following oral dosing. 

1. A compound of formula (I), or a pharmaceutically acceptable salt thereof:

wherein Z₁, Z₂, and Z₃ are each independently selected from H, F, or Cl; Q is O; R² is H; A is a direct bond, —C(O)O*—, —C(R³)(R⁴)O*—, —C(O)O—C(R³)(R⁴)O*—, or —C(R³)(R⁴)O—C(O)O*— wherein the atom marked * is directly connected to R¹, R³ and R⁴ are selected independently from H, fluoro, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or R³ and R⁴ together with the atom to which they are attached form a cyclopropyl group; R¹ is selected from groups [1], [2], [2A], [2B], [3], [4], [5] or [6] wherein the atom marked ** is directly connected to A:

R⁵ and R⁶ are independently selected from H, C₁₋₄ alkyl, C₁₋₄ fluoroalkyl or benzyl; R⁷ is independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl; R⁸ is selected from: (i) H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or (ii) the side chain of a natural or unnatural alpha-amino acid or R⁷ and R⁸ together with the atom to which they are attached form a C₃₋₇ carbocyclic ring; R⁹ is selected from H, —N(R¹¹)(R¹²), or N⁺(R¹¹)(R¹²)(R¹³)X⁻, or —N(R¹¹)C(O)R¹⁴ wherein R¹¹, R¹², and R¹³ are independently selected from H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl, or R¹¹ and R¹² together with the nitrogen atom to which they are attached form a 3-8 membered heterocyclic ring; R¹⁴ is H, C₁₋₄ alkyl, or C₁₋₄ fluoroalkyl; R¹⁰ and R¹⁵ are independently selected from C₁₋₄ alkyl or C₁₋₄ fluoroalkyl; X⁻ is a pharmaceutically acceptable anion.
 2. A compound according to claim 1 wherein A is a direct bond, or —C(R³)(R⁴)O*—.
 3. A compound according to claim 1 wherein R³ and R⁴ are both H, or R³ and R⁴ are both C₁₋₄ alkyl, or R³ is H and R⁴ is C₁₋₄ alkyl.
 4. A compound according to claim 1 wherein R³ is H and R⁴ is methyl, ethyl or isopropyl.
 5. A compound according to claim 1 wherein -A-R¹ has the formula wherein the atom marked ** is directly connected to the oxygen atom:


6. A compound according claim 1 wherein Z₁ is Cl, Z₂ is F, and Z₃ is H; or Z₁ is Cl, Z₂ and Z₃ are H; or Z₁ is H, Z₂ is F, and Z₃ is H; or Z₁ is F, Z₂ is H, and Z₃ is F.
 7. A compound according to claim 1 wherein the compound of formula (I) is selected from: {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}phosphonic acid, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(dimethylamino)acetate hydrochloride, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl acetate, {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl acetate, {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl 2-(dimethylamino)acetate, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-aminoacetate hydrochloride, (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(methylamino)acetate hydrochloride, or ({[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methoxy)phosphonic acid diamine and a pharmaceutically acceptable salt thereof.
 8. A pharmaceutical composition comprising a compound as claimed in claim 1, together with one or more pharmaceutically acceptable carriers and/or excipients.
 9. (canceled)
 10. (canceled)
 11. A method of treatment of a disease or medical condition which benefits from inhibition of gap junction activity, comprising administering to a subject suffering from such disease or condition and effective amount of a compound as claimed in claim
 1. 12. The method as claimed in claim 11 wherein the disease or condition is selected from among migraine, aura with or without migraine, epilepsy, non-epileptic seizures, cerebrovascular accidents including stroke, intracranial haemorrhage (including or traumatic brain injury, epidural hematoma, subdural hematoma and subarachnoid haemorrhage), and intra-cerebral haemorrhage (including CADASIL), spinal cord vascular accidents arising from trauma, epidural hematoma, subdural hematoma or subarachnoid haemorrhage, pain including pain arising from hyperalgesia caused by damage to sensory neurons (i.e. neuropathic pain including but not limited to diabetic neuropathy, polyneuropathy, cancer pain, fibromyalgia, myofascial pain, post herpetic neuralgia, spinal stenosis, HIV pain, post-operative pain, post-trauma pain) or inflammation (including pain associated with osteoarthritis, rheumatoid arthritis, sciatica/radiculopathy, pancreatitis, tendonitis), neurodegenerative disease (including but not limited to Alzheimer's Disease, Parkinson's Disease, Huntington's Disease and Amyotrophic Lateral Sclerosis) and cardiovascular disease including myocardial infarction, coronary revascularization or angina.
 13. A pharmaceutical composition according to claim 8 formulated as a liquid for intravenous dosage.
 14. A pharmaceutical composition according to claim 8 formulated as a solid for oral dosage.
 15. The method as claimed in claim 11 wherein in formula (I) A is a direct bond, or —C(R³)(R⁴)O*—.
 16. The method as claimed in claim 11 wherein in formula (I) R³ and R⁴ are both H, or R³ and R⁴ are both C₁₋₄ alkyl, or R³ is H and R⁴ is C₁₋₄ alkyl.
 17. The method as claimed in claim 11 wherein in formula (I) R³ is H and R⁴ is methyl, ethyl or isopropyl.
 18. The method as claimed in claim 11 wherein in formula (I) -A-R¹ has the formula wherein the atom marked ** is directly connected to the oxygen atom:


19. The method as claimed in claim 11 wherein in formula (I) Z₁ is Cl, Z₂ is F, and Z₃ is H; or Z₁ is Cl, Z₂ and Z₃ are H; or Z₁ is H, Z₂ is F, and Z₃ is H; or Z₁ is F, Z₂ is H, and Z₃ is F.
 20. The method as claimed in claim 11 wherein the compound of formula (I) is selected from: {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}phosphonic acid, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(dimethylamino)acetate hydrochloride, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl acetate, {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl acetate, {[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methyl 2-(dimethylamino)acetate, (3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-aminoacetate hydrochloride, (3S,4S)-6-acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl 2-(methylamino)acetate hydrochloride, or ({[(3S,4S)-6-Acetyl-4-[(3-chloro-4-fluorobenzene)amido]-2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-3-yl]oxy}methoxy)phosphonic acid diamine and a pharmaceutically acceptable salt thereof. 